Fuse structures comprising multiple casings



Oct. 6, 1964 w. s. EDSALL FUSE STRUCTURES COMPRISING MULTIPLE CASINGS Filed Nov. 19, 1962 2 Sheets-Sheet l laweaai'oz Oct. 6, 1964 w. s. EDSALL 3,152,231

FUSE STRUCTURES COMPRISING MULTIPLE CASINGS Filed Nov. 19, 1962 2 Sheets-Sheet 2 Circuit arrangement BF T I Feeder or incoming line United States Patent M 3,152,231 FUSE STRUCTURES COMPRISING MULTIPLE CASINGS William S. Edsall, Boston, Mass, assignor to The Chase- Shawmut Company, Newburyport, Mass. Filed Nov. 19, 1962, Ser. No. 238,466 3 Claims. (Cl. 200-114) This invention relates to electric fuses, and more particularly to electric fuses for elevated circuit voltages and relatively high currents, e.g. circuit voltages in the order of several kilovolts and currents in the order of several hundred amperes. The problem of designing effective fuse structures becomes increasingly difficult with increasing voltage rating and increasing current rating requirements. Conventional fuse structures have a ceiling in regard to voltage rating and current rating. If this ceiling is to be exceeded it is necessary to arrange conventional fuse structures having the required voltage rating in parallel to achieve the required current carrying capacity and interrupting capacity. Such fuse structures, also known as double barrel fuses, are ponderous and bulky.

It is, therefore, one object of this invention to provide fuse structures having relatively high voltage ratings and relatively high current ratings without resorting to paralleling of fuses, i.e. without resorting to structures of the double barrel type.

Another approach to the problem of providing fuse structures having relatively high voltage ratings and relatively high current ratings consists in serially connecting conventional fuses having the required current rating buthaving a voltage rating less than the required voltage rating. The current rating which can be assigned to such series arrangements of conventional fuses is generally substantially less than the current rating of the constituent fuses of the series arrangement when used per se. in addition thereto conventional series arrangements of fuses to increase the voltage rating thereof tend to be bulky and difficult to accommodate in metal clad switchgear or so-called cubicles.

It is, therefore, another object of this invention to provide multiple or composite fuse structures for elevated circuit voltages comprising serially connected fuse units wherein the necessary derating resulting from series connection of fuse units is minimized and which fuse structures are relatively compact and lend themselves well to arrangement in metal clad switchgear or cubicles and to association with circuit breakers for the back-up protection of which they may be applied.

Other objects and advantages of the invention will, in part, be obvious and in part appear hereinafter.

For a more complete understanding of the invention reference may be had to the accompanying drawings wherein FIG. 1 shows a fuse unit embodying the invention and is a section along 11 of FIG. 2;

FIG. 2 shows the same unit as FIG. 1 and is a section along 2-2 of FIG. 1;

FIG. 3 shows diagrammatically the arrangement of a fusible protective device according to FIGS. 1 and 2 in a circuit including a feeder or incoming line and a circuit breaker; 2

FIG. 4 shows in front elevation the arrangement of three units of the type illustrated in FIGS. 1 and 2 in a polyphase circuit; and

FIG. 5 is a top-plan viewof the structure of FIG. 4.

Referring now to the drawings, and more particularly to FIGS. 1 and 2 thereof, reference character 1 has been applied to indicate a pair of tubular insulating casings arranged side by side in parallel relation. Each casing 1 is closed on the ends thereof by a pair of terminal elements in the form of copper plugs 2 which are press- 3,152,231 Patented Oct. 6, 1964 fitted into casings 1. Copper plugs 2 are firmly held in position by radial steel pins 3 projecting transversely through casings 1 into plugs 2. Each of the axially inner surfaces of plugs 2 is provided with a pair of parallel grooves 4. Each pair of radially outer grooves in each casing 1 receives the axially outer ends of a plate 5 of an organic insulating material evolving a gas when exposed to the heat of an electric arc. Plates 5 may be made of a synthetic resin-glass-cloth laminate, e.g. a melamine-glass-cloth laminate. Each pair of radially inner grooves 4 in each casing 1 receives the axially outer ends of a ribbon-type fuse link 6 having a relatively high current-carrying capacity. Fuse links 6 are bent out of the planes defined by the grooves 4 which receive their ends into the plane of the adjacent gas evolving plate 5, and are thus in physical contact with said plate 5. The portions of fuse links 6 in physical engagement with plates 5 are preferably secured to plates 5' by appropriate fastener means (not shown) such as, for instance, staples, or eyelets. Spacer 7 which may be made of Wood impregnated with a synthetic resin separates both casings 1. The two terminal plugs 2 shown to the left of FIG. 2 are conductively interconnected by a metal plate 9, e.g. a copper plate. Each of the two terminal plugs 2 shown to the right of FIG. 2 is provided with a stud or rod-type contact 10. Each of the last referred-to terminal plugs 2 is also provided with an opening into which a wedge element 11 is driven. Wedge element 11 retains in position one end of each of the two restraining wires 12, each arranged inside of one of the casings 1. The opposite end of each restraining wire 12 is attached to one of two indicator pins 13 biased from right to left as seen in FIG. 2 by helical springs 14. Each casing 1 is filled with a pulverulent arc-quenching filler 15, preferably quartz sand. The contact studs or rod-type contacts 10 are cooperatively engaged by tulip-type contacts 16 each formed by a plurality of spring biased contact fingers 1'1. Fingers 17 are arranged in spaced relation and form sleeves into which contacts 10 may enter.

The current path of thestructure shown in FIG. 2 is as follows: Lower tulip-type contact 16, lower stud contact 10, lower right plug 2, lower fuse link 6, lower left plug 2, plate 9, upper left plug 2, upper fuse link 6, upper right plug 2, upper stud contact 19, upper tulip-type contact 16. Restraining wires 12 are made of steelwhich is a metal having a relatively high tensile strength and a relatively high specific resistance, and they have a crosssectional area which is relatively small in comparison to the cross-sectional area of fuse links 6. The latter are made of a metal having a relatively high conductivity, e.g. silver. Hence the resistance of restraining wires 12 is much larger than that of fuse links 6, as a result of which the current normally carried by the fuse-link-shunting restraining wire 12 is very small, or insignificant, in comparison to the current carried by fuse link 6. g

It will be apparent from FIGS. 1 and 2 that the spacing between the two plugs 2 at the right of FIG. 2 and the spacing between tulip-type contacts 16 is very small in comparison to the aggregate length of the two fuse links 6. The reason underlying this discrepancy between the two aforementioned dimensions is due to the fact that a gap which is never ionized (gap between parts 10, or 16, respectively, must have but a relatively short length to achieve a predetermined dielectric strength, but that a gap that has been highly ionized (arc paths in casings 1) must have a much greater length than said relatively short length if substantially the same dielectric strength is to be reached within a relatively short time, e.g. a fraction of the time of a half cycle of a current wave having c.p.s. These are the actual physical facts underlying the structure of FIGS. 1 and 2, since imparting to a series connection of two fuses susbtantially the shape of a U as shown in FIG. 2 results in a relatively small spacing between terminals and a relatively long path for the arcs formed upon blowing of the composite fuse structure.

The effectiveness, or high interrupting capacity, of the fuse structure of FTGS. l and 2 is largely predicated upon the U-shape of the current path through the same and upon the adaptation of the arrangement of parts within casings 1 to the magnetic field set up by virtue of the geometry of the current path through the fuse structure. Upon blowing of the composite fuse of FIGS. 1 and 2 series arcs are formed which follow substantially the geometry of fuse links 6. The arcs thus formed are subjected to electromagnetic action tending to drive the arcs in the direction of the two arrows R away from each other. This tendency is increased by the streams of gas evolving from plates 5 under the action of the arcs kindled immediately adjacent thereto. Thus arcs taking the place of fuse links 6 tend to move by joined magnetic action and gas blast action from the overheated zone of arc initiation into relatively cool pulverulent arc-quenching filler 15. The arc-quenching filler is arranged preponderantly at the opposite sides of fuse links 6 since this is the region into which the products of arcing are being propelled by joint gas blast and magnetic action. It is apparent from FIG. 1 that the spacing L between fuse links 6 is far less than the spacing I etween the longitudinal axes of casings ll. By virtue of this fact the arcs are driven by magnetic action into regions where the cooling of the arcs and of the products of arcing is most intense because of the presence, in this region, of the bulk of the arc-quenching filler 15. It will be apparent from FIG. 2 that the flow of products of arcing in the direction of arrows R is substantially unimpeded, whereas plates 5 form effective gas flow impediments in opposite directions. Thus the flow of hot products of arcing is controlled in such a fashion that they are compelled to fiow in the direction in which they are supposed to flow and where, in view of their expected direction of flow, the bulk of the arc-quenching filler 15 has been concentrated.

Referring now to FIG. 3, this figure shows diagrammatically a circuit breaker CB and a back-up fuse BF embodying the present invention provided for back-up protection of the circuit breaker. The circuit breaker CB and the back-up fuse BF may be part of switchgear of the horizontal draw-out type. The circuit breaker CB has disconnect contacts (not shown) and is movable in the direction of arrow S to the disconnected and the testing positions thereof. The back-up fuse BF is movable in the direction of arrow T from the position shown in FIG. 3 to a disconnected position. shown) between the draw-out mechanism of the circuit breaker CB and the draw-out mechanism of back-up fuse BF precludes moving of the latter to the disconnected position thereof as long as the circuit breaker is not drawn-out and thus disconnected.

Referring now to FIGS. 4 and 5, three fuse units generally designated by reference numeral 2% and being of the type as shown in FIGS. 1 and 2 more in detail and described in connection with these two figures are arranged side by side to control a three-phase circuit. Each fuse unit 24) comprises two tubular casings 1' of insulating material held in spaced relation by spacers 7. Movable plug-type contacts 10' are adapted to cooperatively engage fixed tulip-type contacts 16 and to be disengaged from the latter. Tulip-type contacts 16' are of conventional design and comprise sleeve-forming contact fingers 7' and garter springs 3d biasing contact fingers 7 radially inwardly into engagement with plug-type contacts 10. The three fuse units 20' are held in position by a fuse holder structure including a top member or clamping member 21 and a base member or fuse support 22'. The latter is provided with wheels 23' for moving the three units 20' simultaneously conveniently between their current-carrying position and their drawn-out position. Tie-rods 29' hingedly supported at 28' on base An interlock (not 5 member or clamping member 22 have upper ends engaging slots 24' in top member or clamping member 21'. Helical springs 25' mounted on tie-rods 29' bias latchmembers 27 downwardly into firm clamping engagement with top-member or clamping member 21', thus clamping fuse units 20 between top-member or clamping member 21 and base member or fuse support 22'.

Top-member 21 and base member 22 define registering concave grooves 21a, 22a, adapted to receive fuse units 29'. The grooves 21a, 22a in members 21, 22' are concave and have the same radius of curvature. It will be apparent from FIG. 4 that the grooves 21a in member 21' and the grooves 22a in member 22 are spaced from each other a distance larger than four times the radius of curvature of grooves 21a, 22a.

Blowing of one or more fuse units 2% is indicated by indicator pins 13'. Upon raising of latch-members 27 against the bias of springs 25 tie-rods 29' may readily be pivoted to make it possible to remove top member 21 from the assembly and to obtain access to fuse units 20. The top member 21', the base member 22' and the tie rods 29 are made of an insulating material, preferably a synthetic resin-glass-cloth laminate. Top member 21' and base member 22 must provide sufficient insulation between phases and the lateral spacing between fuse units 20' will increase the higher the voltage between phases. If desired vertical barriers may be arranged between contiguous units 20 to improve interphase insulation.

The structure shown in FIGS. 4 and 5 may be provided with a permanent handle, or a removable snap-on handle. The handle for operating the structure of FIGS. 4 and 5 may also form an integral part of horizontal draw-out switchgear with which the structure of these figures is intended to be associated.

It will be understood that although but one embodiment of the invention has been shown and described in detail, the invention is not limited thereto, and that the illustrated embodiment may be modified or other embodiments made without departing from the spirit and scope of the invention as set forth in the accompanying claims.

I claim as my invention:

1. A fuse and disconnect structure comprising in combination:

(a) a pair of tubular insulating casings arranged side by side in parallel relation and having longitudinal axes having a predetermined spacing;

(b) a pair of terminal elements closing the ends of each of said pair of casings;

(c) a fuse link means arranged eccentrically in each of said pair of casings and conductively interconnecting said pair of terminal elements on the ends thereof, said fuse link means in each of said pair of casings forming a pair of current paths establishing a pair of magnetic fields having longitudinal axes having an average spacing less than said predetermined spacing;

(d) connecting means conductively connecting one of said pair of terminal elements on one of said pair of casings to one of said pair of terminal elements immediately adjacent thereto on the other of said pair of casings;

(e) a pair of movable contacts arranged at adjacent ends of said pair of casings remote from said connecting means, each in coaxial relation to, and integral with, one of said pair of terminal elements on one of said pair of casings;

(f) a pair of fixed contacts each juxtaposed to and cooperatively engaged by one of said pair of movable contacts; and

(g) means for jointly moving said pair of casings and said pair of movable contacts relative to said pair of fixed contacts to cause selective engagement, and disengagement of said pair of movable contacts and of said pair of fixed contacts.

2. A fuse and disconnect structure comprising in combination:

(a) a pair of tubular insulating casings arranged side by side in parallel relation and having longitudinal axes having a predetermined spacing;

(b) a pair of terminal plugs press-fitted into and closing the ends of each of said pair of casings, each plug of each said pair of plugs having groove means on the axially inner surface thereof, the spacing of said groove means in one of said pair of plugs in one of said pair of casings from said groove means in the other of said pair of plugs in the other of said pair of casings being less than said predetermined spac- (c) a pair of ribbon fuse links each arranged in one of said pair of casings and inserted With the axially outer ends thereof into said groove means of said pair of plugs, said pair of fuse links forming a pair of current paths establishing a pair of magnetic fields having longitudinal axes having an average spacing less than said predetermined spacing;

(d) a pulverulent arc-quenching filler inside each of said pair of casings closely surrounding each of said pair of fuse links providing a substantially unimpeded path for the flow for gaseous products of arcing from opposite sides of said pair of fuse links into said filler;

(e) a pair of plate-shaped baflles of a gas-evolving material arranged at juxtaposed sides of said pair of fuse links each in physical engagement with one of said pair of fuse links;

(f) connecting means for conductively connecting one of said pair of plugs on one of said pair of casings to one of said pair of plugs immediately adjacent thereto on the other of said pair of casings;

(g) a pair of movable contacts arranged at adjacent ends of said pair of casings remote from said connecting means each in coaxial relation to, and integral with, one of said pair of plugs;

(11) a pair of fixed contacts each juxtaposed to and cooperatively engaged by one of said pair of movable contacts; and

(1') means for jointly moving said pair of casings and said pair of movable contacts relative to said pair of fixed contacts to cause selective engagement, and disengagement of said pair of movable contacts and of said pair of fixed contacts.

3. A fuse and disconnect structure comprising in combination:

(a) a fuse support of insulating material having a plurality of parallel fusecasing-receiving concave grooves having a predetermined radius of curvature;

(b) a clamping member of insulating material juxtaposed to said fuse support and having a plurality of fuse-casing-receiving concave grooves each in registry with one of said grooves in said fuse support and having the same radius of curvature as said radius of curvature of said grooves in said fuse support, said grooves in said clamping member being spaced from said grooves in said fuse support a distance exceeding four times said predetermined radius of curvature;

(c) a plurality of pairs of tubular insulating casings arranged in the space bounded by said fuse support and by said clamping member, each of said plurality of pairs of casings engaging one of said plurality of grooves in said fuse support and one of said plurality of grooves in said clamping member;

(d) terminal elements closing the ends of each casing of said plurality of pairs of casings;

(e) fuse link means in each casing of said plurality of pairs of casings conductively interconnecting said terminal elements closing the ends thereof;

(1) a plurality of connecting means one on each of said plurality of pairs of casings each conductively interconnecting immediately adjacent terminal elements on one of said plurality of pairs of casings;

(g) a plurality of pairs of movable contacts each arranged at the end of one of said plurality of pairs of casings remote from said connecting means thereof, each contact of said plurality of pairs of contact being arranged in coaxial relation to, and integral with, one of said terminal elements on one casing of said plurality of pairs of casings;

(h) a plurality of pairs of fixed contacts each juxtaposed to and cooperatively engaged by one of said plurality of pairs of movable contacts; and

(1') means for clamping said plurality of pairs of casings between said fuse support and said clamping member to effect joint movement of said plurality of pairs of casings and said plurality of pairs of movable contacts relative to said plurality of pairs of fixed contacts.

References Cited in the file of this patent UNITED STATES PATENTS 635,386 Sacks Oct. 24, 1899 737,284 Sacks Aug. 25, 1903 2,647,970 Edsall et al Aug. 4, 1953 2,885,501 Wood et al May 5, 1959 2,939,934 Kozacka June 7, 1960 2,962,568 Gaskill Nov. 20, 1960 3,116,385 Scott Dec. 31, 1963 FOREIGN PATENTS 156,764 Austria Aug. 25, 1939 528,394 Great Britain Oct. 29, 1940 931,843 Germany Aug. 18, 1955 335,351 Switzerland Feb. 14, 1959 

1. A FUSE AND DISCONNECT STRUCTURE COMPRISING IN COMBINATION: (A) A PAIR OF TUBULAR INSULATING CASINGS ARRANGED SIDE BY SIDE IN PARALLEL RELATION AND HAVING LONGITUDINAL AXES HAVING A PREDETERMINED SPACING; (B) A PAIR OF TERMINAL ELEMENTS CLOSING THE ENDS OF EACH OF SAID PAIR OF CASINGS; (C) A FUSE LINK MEANS ARRANGED ECCENTRICALLY IN EACH OF SAID PARI OF CASINGS AND CONDUCTIVELY INTERCONNECTING SAID PAIR OF TERMINAL ELEMENTS ON THE ENDS THEREOF, SAID FUSE LINK MEANS IN EACH OF SAID PAIR OF CASINGS FORMING A PAIR OF CURRENT PATHS ESTABLISHING A PAIR OF MAGNETIC FIELDS HAVING LONGITUDINAL AXES HAVING AN AVERAGE SPACING LESS THAN SAID PREDETERMINED SPACING; (D) CONNECTING MEANS CONDUCTIVELY CONNECTING ONE OF SAID PAIR OF TERMINAL ELEMENTS ON ONE OF SAID PAIR OF CASINGS TO ONE OF SAID PAIR OF TERMINAL ELEMENTS IMMEDIATELY ADJACENT THERETO ON THE OTHER OF SAID PAIR OF CASINGS; (E) A PAIR OF MOVABLE CONTACTS ARRANGED ADJACENT ENDS OF SAID PAIR OF CASINGS REMOTE FROM SAID CONNECTING MEANS, EACH IN COAXIAL RELATION TO, AND INTEGRAL WITH, ONE OF SAID PAIR OF TERMINAL ELEMENTS ON ONE OF SAID PAIR OF CASINGS; (F) A PAIR OF FIXED CONTACTS EACH JUXTAPOSED TO AND COOPERATIVELY ENGAGED BY ONE OF SAID PAIR OF MOVABLE CONTACTS; AND (G) MEANS FOR JOINTLY MOVING SAID PAIR OF CASINGS AND SAID PAIR OF MOVABLE CONTACTS RELATIVE TO SAID PAIR OF FIXED CONTACTS TO CAUSE SELECTIVE ENGAGEMENT, AND DISENGAGEMENT OF SAID PAIR OF MOVABLE CONTACTS AND OF SAID PAIR OF FIXED CONTACTS. 